In various fields including manufacture of a semiconductor integrated circuit such as LSI, formation of a liquid crystal display device of a liquid crystal display (LCD) panel, manufacture of a circuit substrate such as a thermal head etc., photolithography technology has so far been employed for forming microelements or conducting fine processing. In the photolithography technology, a positive or negative-working photoresist has been used to form a resist pattern and a radiation sensitive resin composition containing an alkali-soluble resin and a radiation sensitive resin composition comprising a quinone diazide compound is well-known as a positive-working photoresist. This composition is disclosed as “Novolak resin/quinone diazide compound” having various formations in many examined patent publications or unexamined patent publications such as Japanese examined patent publication No. Sho 54-23570 (U.S. Pat. No. 3,666,473) and other technical literatures. This kind of photoresist is applied on a silicon substrate, a substrate coated with a film of a metal such as aluminum, molybdenum, and chromium or a substrate coated with a film of a metal oxide such as ITO by the publicly known method such as a spin coat method, a roll coat method, a land coat method, a spray coat method, a dip-coat method to form a thin film, and then a circuit pattern etc. are irradiated using a radiation such as ultra-violet light as an exposure source through a mask pattern. After the exposure to light, a development is conducted to form a resist pattern. Further a fine processing can be made by etching a substrate through this resist pattern as a mask. In this etching process, a resist pattern that performs as a mask requires a sufficient etching resistance.
On the other hand, micronization of wiring width and separation width is further required in the production process recently as a semiconductor device is being highly integrated. In order to respond to this, a process using short wavelength light source which is effective for a high micronization is proposed and partially utilized practically for a light exposure equipment, i.e. a process using deep ultra violet light such as KrF eximer laser (248 nm) and ArF eximer laser (193 nm), further X-ray and electron beams as exposure light source. As the light source is getting in the short wavelength tendency, the material with no absorption in wavelength region to be applied is required for a composition of aforementioned photoresist and, for example, the material such as a chemically amplified type resist based on para-hydroxystyrene is taking a leading position for KrF light source. These kinds of polymer have the problems that they have less etching resistance than the aforementioned novolak resin in general and require etching condition, particularly etching selective ratio between a resist film layer and a layer to be etched, i.e. optimization of etching speed in each layer (to be slowed for a resist and to be fast for an etched layer) and further a deterioration of a pattern-transferred form after etching takes place. Furthermore in order to realize a micronization, a mean to make the resist film thickness thinner upon coating and exposing to light, the aforementioned chemically amplified resist is being used. This makes the etching process more difficult. When using ArF eximer laser light source, acrylic polymers are being proposed wherein an aliphatic cyclic compound is introduced as a material which is transparent to the wavelength used for exposure to light. These polymers were deemed to be further low etching-resistant and made manufacture of a semiconductor device more difficult.
Further, a method to make a resist pattern practically fine using pattern forming equipment so far publicly known are studied. For example in Japanese unexamined patent publication No. Hei 10-73927, a process is described wherein a pattern is formed by the method so far known using a radiation sensitive resin composition so far applied, then a layer is applied on the resist pattern formed, acid generated in a resist by heating and/or exposure to light or acid existing in a resist is diffused into the aforementioned coated layer, the coated layer is crosslinked or hardened by this diffused acid and the resist pattern is made thicker by removal of uncrosslinked coated layer to make the width between resist patterns narrower as a result, to realize the micronization of resist pattern by decreasing separation size or hole diameter and form a fine resist pattern having a higher resolution than the limit of resolution so far known practically. However, it is not mentioned in the patent publication to improve an etching resistance of a resist.
Under the circumstances described above, an object of the present invention is to offer a method to improve etching resistance of a photoresist pattern that is formed by the method so far applied and a method to etch a substrate using the resist pattern as an etching mask, the etching resistance of which is improved.